Rollers or other rotary bodies of a journal bearing are generally held in pockets of one or more annular cages bracketed by shoulders which are designed to prevent or limit any axial excursion thereof. The presence of such shoulders, however, makes a precise machining of the roller tracks difficult. It has, therefore, already been proposed (see, for example, German Pat. No. 1,056,881) to use shoulderless track surfaces and to fit the roller cages with extensions engageable in grooves of the track surfaces for axial guidance.